The properties of both normal erythrocytes and sickle cells are being studied by pulsed nuclear magnetic reesonance. The studies are concerned with the nature and extent of sickle cell hemoglobin (HbS) aggregation. We have found that spin-lattice relaxation time in the rotating frame (T 1 rho) for water protons and for carbon-13 nuclei on HbS is particularly sensitive to the aggregation of HbS into microtubules. Our investigations are involved with the use of T 1 rho measurements to assay the effects of various potential chemotherapeutic agents in preventing microtubule formation; the agents include dimethyl adipimidate, ethyl acetimidate, cynate, and dichloromethane. Quantitative studies of the inhibition of HbS microtubule formation caused by the presence of HbA, HbF, HbC, and HbD, which have been chromatographically prepared, will be carried out. In addition, NMR relaxation times will be utilized to determine the water diffusion rates across erythrocyte membranes, including those from normal cells, ordinary sickle cells, irreversible sickled cells, reticulocytes, and hereditary spherocytes.